1. Field of the Invention
The invention relates generally to a method and apparatus used in underground pilings in the field of foundation repairs, for securing a cable in a piling so that the cable can be used to make the piling more stable.
2. Description of the Related Art
One of the older methods for repairing foundations of buildings having slab-on-ground foundations uses drilled underground piers. Holes are drilled approximately eight to twelve feet in depth and filled with concrete. After the concrete has dried, jacks are placed on top of the pier and the foundation is brought to a level position. The jack is replaced by blocks, shims, and grout. A less expensive method is the use of driven precast solid concrete cylindrical pile sections, which are approximately one foot in height and six inches in diameter. These sections are driven into the earth one on top of the other to form a column or stack of concrete cylinders. The depth to which the bottom of the pier is driven into the earth depends upon the type of soil and zone of the seasonal moisture change. A cylinder having a larger diameter, or a pile cap, is a placed on top of the previously driven sections. Jacks are placed on top of the pile cap and the foundation is lifted.
The precast pile method relies upon the skin friction with the soil for its strength. It has the advantage of being faster since the concrete does not have to cure and precasting allows better control of concrete strength. A major disadvantage is that the one foot cylindrical sections may shift and become misaligned. Different methods have been proposed for maintaining alignment between sections. However, most are methods that must be performed after each piling segment is driven into the ground, and can be time consuming.
The anchoring device in this invention is used to in conjunction with a cable in tension to apply compression to a foundation piling. The compressive state of the foundation piling helps to prevent the individual segments of the foundation piling from slipping or sliding out of alignment. The anchoring device is suspended by a cable into a piling passageway running through all the piling segments. After the anchoring device is lowered to a desired depth, a weight is dropped onto the anchoring device. The force of the weight hitting the anchoring device causes the anchoring device to expand and grip the passageway of the piling. The surface of the anchoring device is textured to prevent the anchoring device from slipping from the piling.
Then tension is applied to the cable. The upward force from the tension is communicated through the anchoring device and into the piling. The upward forces exerted on the lower portion of the piling causes a compressive effect between the upper portion of the piling and the lower portion of the piling. This state of compression helps to prevent the piling segments from sliding relative to each other.
The anchoring device is made up of a centerpiece and at least one anchor wing. The centerpiece has at least one angled face or side that causes the upper portion of the centerpiece to be thinner than the lower portion of the centerpiece. The number of wings depends on how many inclined faces or sides are on the centerpiece. For example, when there are two inclined faces there are also two anchor wings. Each wing is located on the inclined face and is tapered at substantially the same angle as the inclined face. Each wing protrudes above the centerpiece initially. The centerpiece and each wing are held together by a retainer device. When the wings are protruding above the centerpiece and are held in place by the retainer device, the anchoring device is in its initial width position.
The wings protruding above the centerpiece are struck by the weight when the weight is dropped onto the anchoring device. The force of the weight causes the wings to slide down the inclined faces of the centerpiece and also causes the retainer device to disengage from the anchoring device. Each wing slides down the centerpiece along each inclined face, which also causes each wing to travel radially outward. This forces each wing to grip the piling. Ridges or teeth on the outer surface of each wing help to prevent the wings from slipping away from the piling when tension is applied to the cable.